Engine brakes or retarders are used to assist and supplement wheel brakes in slowing heavy vehicles, such as tractor-trailers. Engine brakes are desirable because they help alleviate wheel brake overheating. As vehicle design and technology have advanced, the hauling capacity of tractor-trailers has increased, while at the same time rolling resistance and wind resistance have decreased. Thus, there is a need for advanced engine braking systems in today's heavy vehicles.
Known engine compression brakes convert an internal combustion engine from a power generating unit into a power consuming air compressor.
U.S. Pat. No. 3,220,392 issued to Cummins on Nov. 30, 1965, discloses an engine braking system in which an exhaust valve located in a cylinder is opened when the piston in the cylinder nears the top dead center (TDC) position on the compression stroke. An actuator includes a master piston, driven by a cam and pushrod, which in turn drives a slave piston to open the exhaust valve during engine braking. The braking that can be accomplished by the Cummins device is limited because the timing and duration of the opening of the exhaust valve is dictated by the geometry of the cam which drives the master piston and hence these parameters cannot be independently controlled.
In an effort to maximize braking power, engine braking systems have been developed that use both the compression stroke and what would normally be the exhaust stroke of the engine in a four-cycle powering mode to produce two compression release events per engine cycle. Such systems are commonly referred to as two-cycle retarders or two-cycle engine brakes and are disclosed, for example, in U.S. Pat. No. 4,592,319 issued to Meistrick on Jun. 3, 1986, and in U.S. Pat. No. 4,664,070 issued to Meistrick et al. on May 12, 1987. The Meistrick et al. '070 patent also discloses an electronically controlled hydro-mechanical overhead which operates the exhaust and intake valves and is substituted in place of the usual rocker arm mechanism for valve operation.
A method of two-cycle exhaust braking using a butterfly valve in an exhaust pipe or manifold in combination with opening an exhaust valve at both the beginning and the end of the compression stroke is disclosed in U.S. Pat. No. 4,981,119 issued to Neitz et al. on Jan. 1, 1991.
In a further effort to maximize braking power, systems have been developed which open the exhaust valves of each cylinder during braking for at least part of the downstroke of the associated piston. In this manner, pressure released from a first cylinder into the exhaust manifold is used to boost the pressure of a second cylinder. Thereafter, the pressure in the second cylinder is further increased during the upstroke of the associated piston so that retarding forces are similarly increased. This mode of operation is termed "back-filling" and systems employing this mode of operation are disclosed in the Meistrick '319 patent and in U.S. Pat. No. 4,741,307 issued to Meneely on May 3, 1988.
U.S. Pat. No. 5,526,784 issued to Hakkenberg et al. on Jun. 18, 1996, and assigned to the assignee of the present invention, discloses a system and method for compression braking of a multi-cylinder engine that uses simultaneous opening of all exhaust valves of the engine. The system and method of the Hakkenberg et al. '784 patent, when implemented in a multi-cylinder engine such as, for example, a 6-cylinder engine, provides higher cylinder pressures in cylinders still in the early stages of a compression stroke when the exhaust valves are opened, thereby allowing the cylinder pressure to build up and increase the braking function.
U.S. Pat. No. 5,724,939, issued to Faletti et al. on Mar. 10, 1998, and assigned to the assignee of the present invention, discloses two-cycle and four-cycle methods of compression braking for an internal combustion engine. In accordance with the method disclosed in the Faletti et al. '939 patent, exhaust valves are opened in cylinders wherein associated pistons are near TDC and substantially simultaneously, exhaust valves are opened in cylinders wherein associated pistons are nominally past bottom dead center (BDC). This provides an advantageous braking power increase due to back-filling of the cylinders wherein associated pistons are nominally past BDC.